The majority of current heavy vehicle brake systems use compressed air to apply the brakes. In such systems, control signals are typically transmitted from the driver of the vehicle to the control valves of the brake system, and the brakes are applied. These types of brakes are generally divided into two categories: service brakes and parking brakes. Service brakes are used primarily to slow the vehicle to a stop when the vehicle is moving. Parking brakes are used primarily for helping to prevent the vehicle from moving from a parked position, and may also be used in an emergency situation to slow a moving vehicle when the service brakes have failed, in order to provide a redundant brake circuit.
For service brakes, an operator generally depresses a brake pedal, which in turn actuates a control valve, allowing air pressure to travel to the brake, and the brake is applied. The parking brake is generally engaged by a vehicle operator by actuating a push/pull hand lever within the cab of the vehicle, located on the vehicle dash. The parking brake is generally a spring brake which is normally engaged, meaning that air pressure must be applied to the parking brake in order to release it. parking brake is generally a spring brake which is normally engaged, meaning that air pressure must be applied to the parking brake in order to release it. Thus, when there is no air pressure present, the parking brake is applied. Accordingly, if a vehicle loses air pressure (i.e., ruptured hose, failed component, etc.), and thus loses service brake air pressure and the ability to apply the service brakes, the parking brake will automatically engage, and act to slow a moving vehicle. Likewise, when the vehicle is parked and/or not in use, the parking brake can be engaged by the operator, helping to prevent the vehicle from moving from a parked position.
As mentioned above, typical current day heavy vehicles have a push/pull knob located in the cab of the vehicle which is used to engage and disengage the parking brake. A vehicle may have more than one push/pull knob, depending upon whether there is an additional control for the parking brakes on a trailer attached to the vehicle. The push/pull knob is generally connected to a push/pull double check (PPDC) valve, which controls the flow of air to the parking brake. Generally, when an operator pushes the valve in, it acts to provide air pressure to the parking brake, and thus release the brake, allowing the vehicle to move. In order to apply the brake, the operator pulls the push/pull knob, thus removing air pressure from the parking brake and causing it to engage. Generally, when the knob is pushed in, the air pressure acts to engage the knob and keep it in the pushed in position. Such push/pull knobs also have a feature which allows a manual override where, even if there is a failure in the air system, or the air pressure is not high enough to engage the push/pull knob, the operator may manually hold the knob in to disengage the parking brake and move the vehicle a short distance.
While this is a relatively simple system, it does have several disadvantages. For example, because air lines are routed to and from the switch in the dash of the vehicle, the dash must be relatively large to accommodate the air hoses. Additionally, it can be difficult to install the valve and associated air hoses because of the tight area in which they go behind the dash. Furthermore, maintenance can be difficult in a case where there is an air leak in the valve or associated hoses. The air leak can be difficult to find and repair due to the restricted area of the dash.
These disadvantages are remedied to some extent in numerous prior art references which disclose the that the in-dash PPDC valve can be replaced by a solenoid disposed away from the dash, which solenoid receives electronic control signals from a push button, switch, or the like which is disposed within reach of the vehicle driver (e.g., on the dash of the vehicle). Examples of references which disclose this feature include U.S. Pat. Nos. 6,752,472, 6,322,159, 6,450,587, 6,322,161 and 6,685,281, U.S. Patent Application Publication No. US 2004/0124697 A1, and PCT International Publication No. WO 02/24504 A1. Employing an electronically controlled solenoid rather than the typical in-dash PPDC valve fairly satisfactorily remedies the above-described disadvantages associated with traditional in-dash PPDC valves, while at the same time allowing for advanced features and control schemes to be implemented, such as those disclosed in U.S. Pat. No. 6,322,161 (described in more detail below). However, the brake systems disclosed in all of these references still suffer from a number of disadvantages.
One of such disadvantages relates to the complexity of such systems. Although not fully described in all of the above references, typical heavy vehicle brake systems do not employ only a PPDC valve, but rather also include several additional components and valves, such as a manifold, an inversion valve, an anti-compounding valve, a relay valve, and possibly others. Such systems often require a significant amount of plumbing running in a complex web to connect the various system components. Not only is this large amount of plumbing expensive, heavy and relatively difficult to install (thereby requiring a relatively large amount of time to install), but the potentially long lengths of plumbing between components can lead to delays in achieving required system pressures, such that, for example, parking brake release timing is increased. Moreover, the valves and system components themselves can be expensive, take up a large amount of space, and significantly add to the vehicle's weight.
What is desired, therefore, is a pneumatic brake system for heavy vehicles which does not require a significant amount of plumbing running in a complex web to connect various system components, which does not require plumbing that is expensive, heavy and relatively difficult to install and which can be installed relatively quickly, which does not suffer from long delays in achieving required system pressures such that parking brake release timing is satisfactory, and which does not employ valves and system components which themselves are expensive, take up a large amount of space, and significantly add to the vehicle's weight.